The present invention relates to the art of telescoping masts and, more particularly, to an improved interlocking or latching arrangement between driving and driven flexible link chains which provide a rigid drive assembly for extending and retracting the mast sections.
A telescoping mast and rigid drive assembly of the character to which the present invention relates is illustrated and described in detail in U.S. Pat. No. 5,102,375 assigned to the same assignee as the present application, and the subject matter of which patent is hereby incorporated by reference herein. Basically, the foregoing patent discloses a telescoping mast comprised of a plurality of nested mast sections adapted to be extended and retracted through a rigid drive assembly constructed of two flexible link-type chains, one of which is the driving element of the assembly and the other of which is a driven chain. The driving and driven chains have a common end connected to the innermost mast section, and the two chains are disposed adjacent one another within the mast sections and at right angles to one another with respect to the pivot axes of the links of the two chains. The two chains are fed from corresponding storage positions to a location at which they become parallel for movement together along a linear path generally coaxial with the mast sections and, at the point of linearity, the two flexible chains are latched together so as to provide a rigid drive assembly movable along the linear path to achieve extension and retraction of the mast sections.
In the foregoing patent, the latching arrangements are provided by driving plates secured, such as by welding, across the link plates of adjacent links of the driving chain so as to have abutting edges when the links are in a linear disposition, and alternate ones of the driving plates are provided with notches which are open toward the driven chain of the drive assembly. The link plates of the driven chain which face the driving chain are provided with protrusions secured thereto such as by welding, and extending toward the driving plates, and alternate ones of the protrusions are notched in the direction of movement of the drive assembly for interengagement with the notches in the driving plates when the two chains reach the point of linearity. The others of the protrusions on the links of the driven chain abut against the planar face of the driving plates when the two chains reach the point of linearity. The interengaging notches of the driving plates and protrusions rigidly interengage the two chains against separation laterally of the path of movement and against flexure of the two chains relative to their link axes. The interengagement further provides for the driving chain to displace the driven chain in opposite directions along the path of movement. The protrusions on the driven chain which abut against the drive plates add stability against flexure of the driving chain laterally of the path of movement.
While a latching arrangement of the foregoing character provides an adequate interconnection between the two flexible chains to provide a rigid drive for extending and retracting the sections of a telescoping mast, the notching of the protrusions extending from the driven chain imposes limitations on the load which can be displaced by the drive assembly and, thus, the load which can be utilized in connection with the mast. Furthermore, the welding of the notched drive plates to the driving chain link plates and/or the welding of the protrusions to the link plates of the driven chain is time consuming and expensive in connection with the manufacture of the two chain members. Even if the protrusions are integral with the driven chain link plates and the notched driving plates are integral with the link plates of the driving chain, the provision of such special link plate configurations together with the notching of the protrusions and drive plates is still an expensive procedure and does not overcome the load limitation imposed by the notches in the protrusions on the driven chain. Still further, if one of the notched protrusions or notched driving plates is damaged during use of the drive assembly, replacement thereof is time consuming and difficult and requires disassembly and replacement of at least one entire link section of either or both the driving and driven chains. Accordingly, an inventory of special link sections for both the chains must be maintained for repair and replacement purposes.